DE1228083B - Integrating accelerometer - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY DEUTSCHES Wffl & Wl · PATENT OFFICE

EDITORIAL

Int. CL:

Number:
File number:
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GOIp

GOIc

German class: 42 ο-17

N19832IXb / 42o
April 4, 1961
3rd November 1966

The invention relates to an integrating accelerometer with a pendulum mass, a associated eddy current body, a pick-up device for measuring the angular position of the pendulum, a servo loop with a connected motor that turns a magnet assembly that is used for the Resetting the pendulum acts on the eddy current body, as well as with a counter to count the Engine revolutions.

A device that can provide an indication of speed by integrating accelerations, is desirable in independent navigation as well as in vehicle control. Many types of vehicles, such as B. ships or airplanes, preferably have independent navigation systems that do not require external connection of a physical nature or by means of radiation. The inertial speedometer is one such device. This responds to accelerations and provides precise integration of the Accelerations to show the speed.

The acceleration of any mass is proportional to the force acting on it. When there is a vehicle accelerated, seeks the inertial force acting on an eccentrically mounted mass with reference to cause a deflection on the vehicle. An equally large opposing force is necessary to keep the mass in the undeflected position. The time-related integration of the force that is required to maintain the mass in the undeflected position, the first integral provides the Acceleration experienced by the vehicle. Assuming corrections for some component acceleration, gravity or some other disturbing component the first integral of the measured acceleration is the vehicle speed.

Accelerometers combined with single or double integrators that provide output signals which are proportional to the speed or the distance are already known. These accelerometers are often extremely complicated, difficult to manufacture and assemble in terms of manufacturing technology and highly sensitive to vibrations, loads, temperature changes and others external environmental conditions.

In a known accelerometer of the type mentioned above is a below the Accelerating force moving pendulum-like element provided. The rotation of this element is picked up by a pick-up device, and the resulting electrical signal is via a Servo loop with an amplifier to a servo integrating accelerometer

Applicant:

North American Aviation, Inc.,

Los Angeles, Calif. (V. St. A.)

Representative:

Dr.-Ing. H. Ruschke, patent attorney,

Munich 27, Pienzenauer Str. 2

Named as inventor:

John McElroy Slater, Fullerton, Calif .;

Doyle Ernest Wilcox, Puente, Calif .;

Darwin LeGrand Freebairn, University City, Mo .; Walter L. Pondrom Jr., Houston, Tex.

(V. StA.)

motor given, which reverses the deflection of the pendulum. The revolutions of the engine are counted in a counter for the purpose of displaying the speed.

It is also already known to design the servomotor so that it acts as an eddy current body Acting copper washer works to bring the pendulum back to its rest position by means of the generated eddy currents traced back. The pendulum can be surrounded by liquid.

The known accelerometers have the above-mentioned disadvantage of a complicated structure and high susceptibility to failure.

It is the object of the present invention to overcome these drawbacks and to provide an accelerometer to create that is mechanically more simply constructed and with a low cost of individual parts is robustly constructed.

According to the invention this object is achieved in that the unbalance mass of the pendulum of the Eddy current body is formed.

This results in a much smaller and simpler construction than when using the known one pendulum-like and rotatable unbalance masses.

In the following the invention is based on the drawing for example explained in more detail. It shows

1 shows a representation of the speedometer, which is switched into a servo loop,

Figure 2 is a cross section of a typical embodiment the device according to the invention.

Fig. 1 illustrates the device according to the invention and their servo loop. A servo motor 1

609 709/80

drives a gear 2 and a gear 3, which drive multipole magnets 6 and 7 via a shaft 4. These are arranged very close to a low inertia having rotatable mass 8, the one Has eddy current disk 9. In this illustration, the rotatable mass 8 is eccentric to the axis 11 arranged and therefore subjected to a torque about the axis 11 during acceleration. the Disc 9 is made of copper, aluminum or some other conductive material that is not ferromagnetic is. It is connected to the disc 10, which is attached by means of a low-friction bearing is so that it can rotate about the axis 11. A hole 50 in the disc 9 is sufficient large to allow the passage of the shaft 4. The hole 50 is larger than the shaft 4 and can therefore a small movement of the disc 9 about the axis 11 to. After the disc 9 from a deflection is held by a servo loop, as will be explained later, needs the margin between the shaft 4 and the hole 50 not to be very large. A counterweight 12 is in the disk 10 to adjust the unbalance of the mass 8 inserted. The mass 8, which is attached so that it turns around the axis 11 rotates with a minimum of friction, is about the axis 11 when accelerating in the sensitive direction distracted. The sensitive direction illustrated by arrow 45 is perpendicular to axes 11 and 13.

A removal device 14 and a torque generator 15 cooperate with the rotatable mass 8. The flat coil 16 of the removal device 14 is connected to the disk 10 of the rotatable mass 8 tied together. The electromagnetic element 17, which is a C-shaped armature with a pair opposed wound coils, is the other element of the removal device 14. The electromagnetic Element 17 is excited by an alternating voltage source 18. After an initial setting, the flat coil is in place 16 symmetrical in the field of the element 17, and there is no output signal to the amplifier 19 given. When the rotatable mass 8 is deflected, as it is caused by acceleration, moves the pick-up coil 16 moves with respect to the element 17, and a voltage is induced which is picked up by the amplifier 19. When the spool 16 is unidirectional with respect to the Element 17 is deflected, the amplifier 19 receives a signal with a certain phase. if the coil 16 is deflected in the opposite direction with respect to the electromagnetic element 17 becomes, the amplifier 19 receives a signal of the opposite phase. A phase sensitive one Demodulator 20 receives the output of amplifier 19 and the output of AC voltage source 18, to provide a DC output that varies according to the deflection of the rotatable mass 8. As a result of the storage with low friction and the low inertia of the mass 8, decrease frequencies can occur can be recorded up to several hundred Hertz and demodulated by the demodulator 20. A frequency compensation network 21 receives the output of the demodulator 20. The output signal of the network 21 runs first through the AC solenoid amplifier 22 and then through the phase-synchronized rectifier 23 and is finally applied to the motor 1, which is in this Case is a DC motor. The amplifier 22 and the rectifier 23 can be through a DC amplifier which has reversible output. The motor 1 therefore rotates according to the deflections of the mass 8 and displaces the multipole magnets 6 and 7 in rapid rotation, with eddy currents being induced in the disk 9. These Currents supply a couple of forces and bring the mass 8 back into its starting position. As a result of the rapid response of the engine 1, the mass 8 is in a substantially undeflected position held. At the moderate speeds that predominantly occur during operation (a few revolutions per second) is the force couple developed on the disk 9 or the drag effect of the speed the magnets directly proportional.

The compensation network 21 and the various other elements of the circuit form a closed loop servo control system operating in accordance with known principles for servo mechanisms is trained. The network 21 shown as a delay network is designed so that there is an increase at the lower frequencies provides sufficient responsiveness to the servo system and give stability. In certain cases, the network 21 can be omitted in order to maintain stability. The driven by the gear 2 gear 24 drives the counter 25, which the revolutions of the DC motor 1 counts and gives a direct reading of the speed.

Due to the inertia of the motor, the magnets and the gears, the rotation of the motor 1 can high frequency deflections of the mass 8 do not follow, and therefore these deflections from the Rotation of the motor should not be counted as these frequencies are above the response of the Servo loops. These deflections are extremely undesirable because if there is a deflection, the rotatable Mass is sensitive to accelerations along the axis 13 in addition to those previously described. To achieve greater accuracy, it is therefore advisable to use the mass 8 even at high frequencies hold in a zero position along axis 13, and an additional servo loop is used to achieve this for this purpose the torque generator 15. A switch 26 connects in the switched-on state the output of the demodulator 20 to a compensation network 27 containing the amplifier 28. This Network only allows the passage of higher frequencies and Meiert at higher frequencies greater gain. The signal is fed to the coil 29 of the torque generator 15. One in a row with the coil 29 lying capacitor (not shown) prevents undesired direct current components in the coil 29 flow. Magnets 30 and 30 a, each having a north pole and a south pole have, form the remaining part of the torque generator 15. Thus, the applied to the coil 29 act Signals as a speed damping means that prevents the mass 8 from accelerating to be deflected at higher frequencies «Increase in the viscosity of the swimming fluid (mentioned below in connection with Fig. 2) is another way of achieving this a speed damping agent to reduce the sensitivity to accelerations of high frequencies to diminish. The increase in the moment of inertia of the pendulum also causes a reduction in sensitivity to high

5 6

frequent accelerations. As a result, the calculation of the exact relationships so that

Distractions of lower frequencies due to the lift change with the change in conductivity

Speech properties of the motor 1 and deflections of the temperature compensated, is the following:

of the other higher frequencies at a minimum L = Mr χ oVr χ (V)

held by the damping means. There are therefore 5 ^{1 2} '

in the illustrated embodiment, two ge with

closed loop servo circuits available. The torsional L = torques acting on a rotating mass

number of motor 1 is an indication of the effect that accelerates in a fluid

acceleration. The shaft position of the motor 1 becomes;

or the rotation read on the counter 25 M = floating mass;

number is an indication of the speed of the front r _x = distance between pivot point and

direction. Center of gravity of the crowd;

Fig. 2 is a cross section of a typical out x = acceleration in the sensitive direction

management form of the device according to the invention. tung;

The motor 1 drives a gear 2, which in turn has an i5 V = volume of the floating in the fluid

Gear 3 drives. The shaft 4 is grounded in the housing;

and attached to an aluminum hub 31, r ₂ = distance between the pivot point and

to which a magnet group 6 is attached. One equal to the center of lift;

like aluminum hub 32 supports a group of magnets 7. ρ = fluid density.

When the temperature changes, the magnetic field can ²⁰ CII. j * * τ- * ι.

of magnets 6 and 7 change considerably. The * P equal and opposite torque

Aluminum hubs 31 and 32 form a device T ™ 1 ff ^Mag ^ ⁿ PJ ^{1 efert} '^ ^Str ° ^m _A ^lT \

to compensate for the change in the magnetic ^{strength of the} eddy current disc induce so that the pendulum

with temperature. The coefficient of thermal expansion is ^{maintained independently of the deflection:}

ent of the hubs 31 and 32 and the hub shape grain 25 __ ω _ 'n \

compensate the change in magnetic strength by * ~~ ~ r ~ ~ ' ^ -'

Changing the distance between the magnets whereby

at different temperatures. A practical

The linear output of the measuring device is thus despite ^L i = torque created ^{by induction;}

Receive temperature changes. 30 K = a constant;

According to FIG. 2, the rotatable mass 8 is immersed in ^ω = angular velocity of the magnets;

a liquid-tight compartment and is on a shaft 35 ^r = coefficient of the specific resistance of the

arranged by means of a liquid bearing. A disk.

Pump 33 delivers liquid, such as ζ B. Petroleum _Put equations (1) and (2) together

or a fluorinated hydrocarbon, 35 ^

to a pipeline 34 which is equal to 35 from the center of the shaft and solving for - on, thereby floating the Benach runs down and divided _schleumgung with respect to the hub 36 by the angular velocity. The rotatable mass 8 lies in one of the magnets (which should remain a constant, liquid-tight chamber 37. A return line 38 _{so that there is a constant} scale factor): runs from the chamber 37 to the pump 33. The 40

Disk 9 is located in the part of chamber 37, * _{Λ r} -λ _v "" ν _ ν ^ω / o \

which lies between the magnet groups 6 and 7. The r

Shaft 4 runs through a hole in disk 9 with ... "

a margin greater than the maximum Ab- J ^ - (Mr ₁ -Vr ^ q) = -, (4)

steering is what the mass 8 experiences. 45 ^{ω r}

The disc 9 is made of materials such as aluminum ^ ^

or copper, with good electrical and thermal - = ■ = constant. (5)

Conductivity. The higher the conductivity, the more ^ω r {Mr _x - Vr ₂ Q)

The available torque is greater, and so is the following relationship _{when the temperature changes}

the unbalance of the mass 8 can be higher. 50 _apply known _fa u _s, the ratio in equation (5)

Metals and alloys with high conductivity should _{remain constant} : also have a large change in conductivity with the

Temperature, which the sensitivity of the instru- r {Mr _x - Fr ₂ ρ) = constant. (6)

mentes can directly influence funds must be seen before- _{The specific wide} rstand r is: to be seen around this change in conductance with 55

to compensate the temperature to the application r - r _o (l + at), (7)

from non-magnetic materials of high conductivity to being

enable. This is done in the device, e.g. B. r ₀ == specific resistance without temperature according to Fig. 1, by a corresponding design change;

achieved to compensate for this change. Determine 60 _a _ temperature coefficient of the specific certain liquids, such as B. the means mentioned, resistance; have a suitable change ratio of density t - temperature change with temperature for a corresponding compensation. The idea, then, is a means to comparable ^u _. . . “Turn that the buoyancy or the buoyancy 65 S = Qo U - ^b U > (°) and thus the imbalance of the eccentrically arranged whereby

Mass changes to the change in conductivity of ρ ₀ = initial density without temperature change;

Compensate disc exactly. b = temperature coefficient of fluid density.

Substituting (7) and (8) into (6) one gets:

r ₀ (1 + αt) [Mr ₁ - Vr ₂ -Q ₀ (I- bt)]

[r ₀ + r _o at] [Mr ₁ - Vr ₂ ■ Q ₀ + Vr ₂ Q ₀ bt]

[T ₀ Mr ₁ -r ₀ Vr ₂ Q ₀ + r ₀ Vr ₂ Q ₀ bt + r _o at M V ₁ - r _o atV'r ₂ Q ₀ + r ₀ atVr ₂ - Q _o bt \

Taking the derivative and setting it equal to zero to solve for the case where the equation is a constant one gets:

constant, (9) constant, (10) constant. (11)

r _Q Vr ₂ Q _o bdt

- r ₀ aVr ₂ ■ Q _o dt + r ₀ aVr ₂ Q ₀ b2tdt = 0.

Removing the common factor r ₀ and dt and neglecting the smaller term results in:

Vr ₂ Q ₀ b +

Vr ₂ Q ₀ (Pa)

Vr ₂ Q ₀ Mr ₁

ο,

-UMr ₁ ,

away '

(12)

Equation (12) illustrates the relationship that the parameters of volume, r ₂ , Q ₀ , mass and r _x must have with one another in order for the thermal coefficients of resistivity and fluid density, α and b, to compensate for one another. It is noted that Vr ₂ Q _{0 is} the buoyancy imbalance of the rotatable mass 8 and Mr _{1 is} its mass imbalance. It can be noted that the volume imbalance would then be Vr ₂ . The volume imbalance, of course, has a predetermined ratio to the buoyancy imbalance, the ratio being the fluid density Q. Therefore, equation (12) expresses the relationship of the lift imbalance to the mass imbalance if temperature compensation is to be achieved. The compensation consists in the fact that the change in the disk conductivity due to the temperature is compensated for by the change in the fluid density.

Claims (5)

Patent claims: 1. Integrating accelerometer with a pendulum mass, one connected to it Eddy current body, a measuring device for measuring the angular position of the pendulum, a Servo loop with a connected motor that rotates a magnet assembly that is used for resetting of the pendulum acts on the eddy current body, as well as with a counter for counting of the motor revolutions, characterized in that the unbalanced mass of the pendulum is formed by the eddy current body. 2. Accelerometer according to claim 1, characterized in that the magnet arrangement two permanent magnets rotated in the same direction and arranged on both sides of the eddy current body having. 3. Accelerometer according to claim 2, characterized in that the eddy current body is designed as a circular disc provided with a central opening and the Magnets are arranged on an axis passing through the opening. 4. Accelerometer according to claim 1, characterized in that the eddy current body is arranged in a fluid, the buoyancy imbalance and the mass imbalance of the eddy current body has a predetermined relationship to the temperature coefficient of the specific Resistance of the eddy current body in the magnetic field and the temperature coefficient the fluid density of the fluid so as to compensate for the effects of temperature on the device. 5. Accelerometer according to claim 4, characterized in that the predetermined Relationship of the lift imbalance to the mass imbalance equal to the ratio of the temperature coefficient the resistivity of the eddy current body divided by the difference between the temperature coefficient of the resistivity of the body and the Is the temperature coefficient of the fluid density of the fluid. Considered publications:
German Auslegeschrift No. 1035 370;
French Patent No. 1212 770;
U.S. Patent Nos. 2,853,287, 2,933,298, 964,949. Legacy Patents Considered:
German Patent No. 1125 690. 1 sheet of drawings 609 709/80 10.66 © Bundesdruckerei Berlin